Digital subscriber line (xDSL) technology has developed in recent years in response to the demand for high-speed Internet access. xDSL technology utilizes the communication medium of pre-existing telephone systems. Thus, both plain old telephone systems (POTS) and xDSL systems share a common line for xDSL-compatible customer premises. Similarly, other services such as time compression multiplexing (TCM) integrated services digital network (ISDN) can also share a common line with xDSL and POTS.
In the field of telecommunications, the term crosstalk refers to interference that enters a message channel or disturbed channel from one or more other interfering channels (or disturbing channels) through a path coupling the interfering channels to the message channel. Crosstalk leads to reduced signal-to-noise ratio (SNR) that can create low audio quality in a voice system or reduced data rates and/or increased errors in a data system.
There are many types of crosstalk mechanisms on xDSL lines that are characterized, the two main types being far end crosstalk (FEXT) and near-end crosstalk (NEXT). FEXT refers to electromagnetic coupling that occurs when the receiver on a disturbed pair is located at the far end of the communication line relative to the transmitter of a disturbing pair. Self-FEXT generally refers to interference caused by neighboring lines provisioned for the same type of service as the affected line, although the neighboring lines and the affected line may be provisioned for different services as well. In contrast, NEXT results from a disturbing source connected at one end of the wire pair which causes interference in the message channel at the same end as the disturbing source.
Allocations of wire pairs within telephone cables in accordance with service requests have typically resulted in a random distribution of pair utilization with few precise records of actual configurations. Because of the physical proximity of different twisted pairs within a cable bundle (due to pair twisting, cable branching, cable splicing, etc.), crosstalk caused by the electromagnetic interference between the neighboring lines is often the dominating noise source in the transmission environment. In addition, due to pair twisting in cables where cable branching and splicing take place, a wire pair can be in close proximity to many different pairs spanning different portions of its length. At a telephone CO (central office), pairs in close proximity may carry diverse types of service using various modulation schemes, with considerable differences in signal levels (and receiver sensitivities) especially for pairs of considerably different lengths.
Both FEXT and self-FEXT continue to be a problem in xDSL communication systems as crosstalk impacts overall performance. Current approaches to addressing crosstalk suffer from various perceived shortcomings, such as increased design costs, high memory usage, and considerably increased need for computational resources along with their inefficient usage. Therefore, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.